Elo rating

elo.pl

#!usr/bin/perl env
use strict;
use warnings;
use 5.010;
use Math::Round;

my $k = 32;

my %winner = (
	'name' => 'John',
	'score' => 1500,
	'win' => 0,
	'lose' => 0,
);

my %losser = (
	'name' => 'Mike',
	'score' => 1500,
	'win' => 0,
	'lose' => 0,
);

for (my $var = 1; $var <= 100; $var++) {
	my $win_expected = expected($losser{'score'}, $winner{'score'});
	my $win_new_score = win($winner{'score'}, $win_expected);
	$winner{'score'} = $win_new_score;

	my $lose_expected = expected($winner{'score'}, $losser{'score'});
	my $lose_new_score = lose($losser{'score'}, $lose_expected);
	$losser{'score'} = $lose_new_score;

	say "$var : Winner score: ".nearest(1,$winner{'score'});
	say "$var : Losser score: ".nearest(1,$losser{'score'});
}

sub expected {
	my ($Rb, $Ra) = @_;
	return 1 / (1 + (10 ** (($Rb - $Ra) / 400)))
}

sub win {
	my ($score, $expected) = @_;
	return $score + $k * (1 - $expected);
}

sub lose {
	my ($score, $expected) = @_;
	return $score + $k * (-$expected);
}


=pod
    Ra -- Rate of player A
    Rb -- Rate of player B
    K -- K-factor : レートの補正の最大値
    http://en.wikipedia.org/wiki/Elo_rating_system
=cut